Process and apparatus for the separation of gases by rectification



Jan. 3, 1939. J. KOPP 2,142,446

PROCESS AND APPARATUS FOR THE SEPARATION OF GASES BY RECTIFICATION Filed Aug. 27, 1935 TiE- INVENTOR ATTORN S.

Jan. 3, 1939 OFFICE,

rmcass m arrana'rus FOR "rrm suranterior: or cases BY nucnrrca'rrou.

. 131m Kopp, Grosaheaselohe, near Munich, Germany, assignmto Geaellschaft fiir Lindes Fine: maschinen-A. G., Hollriegeiakrcnth, near HnnIcLGermany Application August 21, 1935, Serial No. 38,118

In Germany September 8'7, 1934 8Ciaima.

An object of the present invention is to provide an apparatus and a method of operating the same whereby the pressure required for the lique:

faction of nitrogen in heat exchange with the liquid oxygen to be vaporized in processes for the separation of the oxygen and nitrogen contents of air by liquefaction and rectification is minimined. The invention is designed principally for improving the operation of a rectifying apparatus comprising at least two columns, or the column of which. is divided into two parts, by a heat exchange device or condenser-vaporizer for bringing the gaseous nitrogen from the lower column into heat exchange with the liquid oxygen from the upper column for the purpose of vaporizing" the oxygen and liquefying the nitrogen. k

of pipes connected into suitable headers and to 2 bring about the heat exchange between the liquid oxygen and the gaseous nitrogen by passing the nitrogen through the tubes and the oxygen in contact with the outside of the tubes. In recent years this arrangement has been almost universally accepted.

It has now been found that the heat transfer in the condenser-vaporizer can be improved and the pressure required for the liquefaction of the nitrogen correspondingly reduced by reversing the positions of the oxygen and nitrogen with respect to the heat transfer tubes, i. e. by contacting the liquid oxygen with the inside of the tubes 7 and the gaseous nitrogen with the outside of the tubes. The results obtained are quite surprising, since no reason is at present apparent why the heat exchange should be more eflicient in one direction than in the other through the walls of the heat exchanger.

It has been found that the temperature difference of about 3' C. usually required in a condenser-vaporizer in which the nitrogen is condensed on the inside of the tubes which are bathed on theoutside by liquid oxygen may be materially reduced. This temperature difierence corresponds to a pressure difference, depending upon thepurity of the recovered oxygen, of about 0.6 to -1.2 atmospheres and it is found that a reduction of this pressure difference by only a few tenths of an atmosphere results in a saving in energy required for the whole rectification process of from to It has iurther been found to be advantageous to have the oxygen to be vaporized enter the tubes of the condenser-vaporizer from below and toprovide for a circulation of this liquid oxygen through the tubes.

The method will be described, more fully and illustrated in connection .with the two embodiments of the invention illustrated in the accompanying drawing, in which:'

Fig. 1 is a diagrammatic vertical sectional view of a two-stage rectifying column in which the condenser-vaporizer is a bundle of straight tubes, and l Fig. 2 is a diagrammatic vertical sectional view of apparatus having a modified type of condenser-vaporizer.

Referring to Fig. 1 of the drawing, i is the lower column, 2 theupper colunin, and 8 the condenser-vaporizer connecting the upper part of x the lower column with the lower part of the upper column to provide a two-stage rectifying appara- 'tus. The liquid oxygen collecting on the bottom plate 4 of the column 2 flows through the pipes 5 and 8 to the header from which it passes upwardly through -the bundle of tubes 8 into the chamber 9. By means of this arrangement the liquid oxygen delivered into the chamber 9 by pipe 5 is caused to continuously circulate through pipe 6, header I, tubes 8, and chamber 9. 1 The oxygen vaporized and rising in tubes 8 actuates this circulation and the rapid movement of the liquid oxygen through tubes 8 promotes the heat transfer. Gaseous oxygen formed in pipes 8 collects in the chamber 9 above the level of the liquid therein and one portion passes out as pure oxygen by way of the pipe I0 while the rest rises in the upper column. The outside of the bundle of tubes'8 is bathed by gaseous nitrogen rising from the lower column I through the uppermost plate of the lower column I and one portion of the liquid nitrogen collecting on the plate H is delivered through pipe l2 into the upper portion of the upper column 2 as is customary, while the rest flows downwardly as a washing liquid in the lower column. Plates 4 and H are of the usual construction and are conventionally illustrated as simple perforated plates. The lower column-may be provided with the customary arrangements including an air inlet pipe l9 having a coil portion in the liquid at the base of the column and an expansion valve and a liquid transfer conduit 20 for conducting liquid from the base of-the lower column I to a mid portion of the upper column 2.

In the apparatus illustrated in Fig. 2 the liquid oxygen from the upper column 21 is delivered into the header ll at its lower end at such a rate that it is completely vaporized in passing through the coils I5 of the condenser-vaporizer 23 and the resulting gaseous oxygen passes out of the condenser-vaporizer at its lower header It. At the same time gaseous nitrogen is delivered to the condenser-vaporizer II from the lower column ll through the relatively large pipe l1, and liquid washing liquid for the lower column 2!. The oxygen is conducted from header ll through apipe 24 to the lower portion ll of theupper column 12 in order to supply a gas phase for the upper column. The oxygen product is withdrawn through conduit "that may connect to the pipe 24. geous when the liquid oxygen and gaseous nitrogen-are not of uniform composition.

It will be understood that the condenser-vaporizer, for the sake of clearness, has been illustrated only diagrammatically. The details of the construction of the condenser-vaporizer, especially the number and size of the heat exchange tubes,- may be designed in accordance with well known practice and forms no part of the present invention.

This embodiment is particularly advanta- The process or method has been described particularly with reference to the separation of the oxygen and nitrogen of air, but the invention embraces, as will be apparent the separation of the component gases of other analogous gas mixtures.

I claim: a

1. Process for the separation of a mixture of at least two gases in which the mixture of gases is subjected to a first rectification under pressure, the liquid product of said first rectification is subjected to a second rectification at lower pressure and the liquid product of said second rectification is brought into heat exchangawith the gaseous product of the first rectification to vaporize the former and 'liquefy the latter, the step which consistsin effecting the liquefaction of all of the gaseous product of said first rectification exclusively by contact with the outside of heat transfer tubes through which the liquid product 0f the second rectification passes.

.lProcessasdefinedinclaimdinwhichtheliquid product of the second rectification is continuously passed upwardly through the heat transfer .tubes, the resulting gaseous and liquid portions separated, the'gaseous portion with-,

drawn, and the liquid portion returned to the lower end of the tubes in a continuous cycle whereby circulation of saidliquid is promoted by the partial vaporization of the liquid in said tubes.

3.Process asd'efinedinclaim 1 inwhich the liquid product of the second rectification is delivered to the heat transfer tubes at such a rate that'substantially complete vaporization thereof is brought about by a single passage of the liquid through said tubes. f

4. appma'a for the separation of the components of a gas mixture by rectification comprisingan upper rectifying column, a lower rectifying column, and an intermediate condenservaporizer comprising heattransfer tubes, means for passing the entire liquid product of the upper rectifying column through said tubes, and means for effecting the liquefaction of all of the gaseous product of said first rectification solely by passing said product in contact with the outside of said tubes.

- 5. Apparatus for the separation of the components of a gas mixture by rectification comprising an upper rectifying column, a lower rectifying column, an intermediate condenservaporizer comprising upper and lower chambers connected by a bundle of tubes, means for delivering liquid from the upper rectifying column into the upper of said chambers, means for delivering liquid from said upper chamber out of contact with said bundle of tubes to the lower chamber, means for withdrawing gas from said upper chamber, a jacket surrounding said bundle of tubes and forming a closed housing, and means for delivering gasfrom the lower rectifying column into said housing.

6. Apparatus for the separation of the components of a gas mixture by rectification comprising an upper rectifying column, a lower rectifying column, an intermediate condenservaporizer comprising a plurality of coils, a jacket surrounding said coils and forming a closed housing, means for passing the entire liquid product from the upper rectifying column downwardly through said coils, and means for delivering gaseous product from the lower rectifying column into said housing.

JULIUS KOPP. 

